Cross-linked thermoplastic polyurethane/polyurea and method of making same

ABSTRACT

A process for forming a cross-linked thermoplastic polymer is disclosed herein. The cross-linked thermoplastic polymer is formed by heating a first mixture containing a thermoplastic urethane base material, a monomeric diisocyanate comprising between 1 to 10% of the total weight of the first mixture, and a second mixture of a first diamine and a second diamine comprising between 1 to 10% of the total weight of a total reaction product. The heated first mixture, which is flowable, is injected into at least one injection molding device, with the second mixture injected at predetermined intervals to create a homogeneous reaction product.

CROSS REFERENCES TO RELATED APPLICATIONS

The Present application is a continuation application of U.S. patentapplication Ser. No. 12/260,279 filed on Oct. 29, 2008, which is acontinuation-in-part application of U.S. patent application Ser. No.12/184,394 filed on Aug. 1, 2008, which is a divisional application ofU.S. patent application Ser. No. 10/992,907 filed on Nov. 18, 2004, nowU.S. Pat. No. 7,417,094.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention generally relates to thermoplasticpolyurethanes and thermoplastic polyureas having properties similar tothose of castable or cross-linked polyurethanes or polyureas. The fieldof the invention also includes methods of making the same.

2. Description of the Related Art

There currently are a number of commercialized products made frompolyurethanes and polyureas. Typically, these products made from eitherthermoplastic polyurethanes (or polyureas) or thermoset polyurethanes(or polyureas). Thermoplastic polyurethanes generally have linearmolecular structures and are able to flow freely at elevatedtemperatures. For this reason, thermoplastic polyurethanes are preferredfor products which are produced by injection molding or other extrusiontechniques, where flowability of the reactants are of paramountimportance. Unfortunately, thermoplastic polyurethanes typically exhibitpoor performance characteristics with respect to abrasion, tensilestrength, rebound, and compression set compared to castablepolyurethanes.

In contrast to current thermoplastic polyurethanes, thermosetpolyurethanes have particularly good characteristics with respect toabrasion, tensile strength, rebound, and compression set. Thermosetpolyurethanes generally have a network structure that incorporatesirreversible chemical cross-linking. The downside of thermosetpolyurethanes is that the irreversible chemical cross-linking reactionmakes it unsuitable for use in injection molding and extrusionapplications. Typically, thermoset polyurethanes are formed using acasting process. Unfortunately, casting processes require costlyequipment and usually involve a large number of processing steps.Casting is thus a less efficient and more expensive method of producingpolyurethane-based and polyurea-based products as compared to injectionmolding and extrusion systems.

In a typical process for making a thermoset (i.e., castable)polyurethane, a di-isocyanate component is first pre-polymerized with apolyol having either a polyester or polyether backbone. The remainingdi-isocyanate of the pre-polymer is reacted with a chain extender or across-linking agent or a blend of cross-linking agents. Catalysts areadded to control the reaction rate. If the cross-linking agent has adihydroxy functional component, a polyurethane will be formed. If thecross-linking agent has diamine functionality, a polyurea is formed.

With respect to thermoplastic polyurethanes, a diol or polyol is reactedwith an isocyanate. This reaction typically takes place in largecommercial reactors. As stated above, thermoplastic polyurethanes, whilenot cross-linked, are usable in injection molding and other extrusionmethods. Because of the lack of cross-linking, these materials haveabrasion, tensile, and compression set properties that are not as goodas thermoset polyurethane or polyurea systems.

There thus is a need for a thermoplastic polyurethane or polyureamaterial which exhibits good abrasion, tensile strength, rebound, andcompression set characteristics which are similar to those found inthermoset urethanes. Such a material could be produced usingconventional injection molding and/or extrusion techniques, therebyreducing the cost of manufacture for the material.

The conventional solution has been to add a cross-linking agent to athermoplastic resin, either post-injection molding or pre-injectionmolding. Adding the cross-linking agent pre-injection molding allows fora greater dispersion of the cross-linking agent within the thermoplasticresin material. However, many cross-linking agents have low boilingtemperatures and will “flash off” prior to dispersion, especially atroom temperatures. Trying to add other agents to resolve the flash offproblems leads to other processing issues, especially with injectionmolding machines which melt processing materials (thermoplastic resins)and inject the melted materials under high pressures to form variousarticles, which can lead to a build up of materials in the injectionmolding barrel.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a solution for forming cross-linkedthermoplastic polymers. The present invention adds a cross-linking agenta thermoplastic resin in the pre-injection molding stage. In order toprevent the cross-linking agent from flashing-off, a second mixture isadded during the injection molding stage. This second mixture preventsthe flashing off of the cross-linking agent while allowing forprocessing without a build-up of material.

One aspect of the present invention is a method for forming an articlecomposed of a cross-linked thermoplastic polymer. The method includesmixing a thermoplastic urethane based material and a monomericdiisocyanate to create a first mixture. The monomeric diisocynatecomprises between 1% to 10% of the total mass of the first mixture, thediisocyanate. The method also includes mixing 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) and diethyl2,4-toluenediamine to create a second mixture. The 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) is 75% to 95% of the totalmass of the second mixture and diethyl 2,4-toluenediamine is 25% to 5%of the total mass of the second mixture. The method also includesheating the first mixture to a temperature within the range of 250° F.to 550° F. to created a heated first mixture. The method also includesheating the second mixture to a temperature greater than the meltingpoint of the second mixture and less than 225° F. to create a liquidsecond mixture having a volume. The method also includes injecting theheated first mixture into a barrel of an injection molding machinethrough a first opening. The method also includes injecting the liquidsecond mixture into the barrel of the injection molding machine in aplurality of dispensing shots of approximately equal amounts of thevolume of the liquid second mixture during a predetermined time period.The method also includes injecting a reaction product into at least oneinjection mold cavity, the reaction product formed by the reaction ofthe heated first mixture and the liquid second mixture. The method alsoincludes forming an article composed of the reaction product.

Having briefly described the present invention, the above and furtherobjects, features and advantages thereof will be recognized by thoseskilled in the pertinent art from the following detailed description ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 schematically illustrates an injection molding device which canbe used to produce products made from cross-linked thermoplasticpolyurethanes/polyureas according to the present invention.

FIG. 2 is a flow chart of a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The method for forming a cross-linked thermoplastic polyurethane orpolyurea generally involves four different components. The firstcomponent is a thermoplastic polyurethane resin material. The secondcomponent is a diisocyanate. The third component is a diamine. Thefourth component is a diamine.

The thermoplastic polyurethane resin material and the diisocynate arepreferably mixed in a dry state to create a first dry mixture. The thirdand fourth components, the diamines, are mixed together to create aliquid second mixture. The dry mixture is heated into a flowable formand the liquid second mixture is introduced at predetermined intervalsof equal amounts to create a homogeneous reaction product.

The thermoplastic polyurethane base material may include TEXIN 985, anaromatic polyether-based thermoplastic polyurethane available from BayerCorporation. As another example, the thermoplastic urethane basematerial may include NOVEON ST80A, which is available from NoveonIncorporated. Another thermoplastic polyurethane is IROGAN A 95 P 4021from Huntsman Chemical. IROGAN A 95 P 4021 is a thermoplasticpolyether-polyurethane having a Shore A hardness of approximately 95, aShore D hardness of approximately 46, a melt index of 210° C./21.6kilograms at 5-15 grams/10 minutes. Another thermoplastic polyurethaneis TEXIN DP7 1197 from Bayer Corporation. TEXIN DP7-1197 is athermoplastic polyester polyurethane having a Shore A hardness of 88.Another thermoplastic polyurethane is DESMOPAN 445 from BayerCorporation. DESMOPAN is a thermoplastic polyester polyurethane having aShore D hardness of 45.

The thermoplastic urethane base material is preferably dried prior toadding the additional components described in detail below. This can beaccomplished, for example, by heating the thermoplastic base material toa temperature between about 100° F. to 200° F. in a separate container.

A monomeric diisocyanate is added to the dried thermoplastic urethanebase material. Preferably, the diisocyanate used in the process is asolid at room temperature. In one preferred aspect of the invention, thediisocyanate is 4,4′ diphenylmethane diisocyanate, which has asublimation point of approximately 392° F. This can be commerciallyobtained from Bayer Corporation under the trade name, MONDUR M (CAS No.101-68-8). Preferably, the flaked or fused form of MONDUR M is used inconnection with the process described herein. The diisocyanate ispreferably stored at about −20° C. By adding diisocyanate to thethermoplastic urethane base material, isocyanate functionality is addedto the system. Other Diisocyanate materials which are solid at roomtemperature and may be used in accordance with the invention include:Toluene Diisocyanates (TDI), Toluene ortho Diisocyanates (TODI),Naphthalene Diisocyantaes (NDI), Hydrogenated Methylene Diisocyantaes(H12MDI), Iso Phorone Diisocyanates (IPDI), Hexamethylene Diisocyantes(HDI). These isocyanate-based compounds can be made in solid crystallineform suitable for dry blending. These isocyanates can also be added inthe liquid and semi-liquid form.

Preferably, the diisocyanate comprises between 1% to 10% of the totalweight of the mixture forming the cross-linked thermoplasticpolyurethane/polyurea. Even more preferably, the diisocyanate comprisesbetween 1% to 2% of the total weight of the mixture forming thecross-linked thermoplastic polyurethane/polyurea. The diisocyanatematerials other than those specifically identified above may also beused in accordance with the invention, provided they exist as a solid atroom temperature.

One preferred diamine is 4,4′methylene-bis-(3-chloro-2,6-diethylaniline), available commercially asLONZACURE M-CDEA (CAS No. 106246-33-7). Another diamine which can beemployed with the present invention is 4,4′Methylene-bis-(2,6-diethylaniline), available commercially as LONZACUREM-DEA (CAS No. 13680-35-8). Both diamines have melting points atapproximately 90° C. Preferably, the diamine is added in solid form anddry blended with the MDI and thermoplastic urethane base material.Alternative cross-linking agents and other solid or crystalline Diamineswhich may be used in the present invention include: MOCA(4,4′-Methylenebis-(O-Chloroaniline)), MDA (Methylene Dianiline), aswell as any other methylene bis aniline like LONZACURE M-CDEA describedabove. Any other diamine-based compounds can be made in solidcrystalline form suitable for dry blending can also be used. Thediamines above can also be added in the liquid or semi-liquid form.

A second diamine for the second mixture is preferably diethyl2,4-toluenediamine, which is available under the brandname ETHACURE 100,or E100, from Albermarle of Baton Rouge, La. The diethyl toluene diamineprevents build-up due to the first diamine, preferably 4,4′methylene-bis-(3-chloro-2,6-diethylaniline). The second mixture ispreferably 75 to 95 parts by weight 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) and 5 to 25 parts by weightdiethyl 2,4-toluenediamine, and more preferably 80 to 90 parts by weight4,4′ methylene-bis-(3-chloro-2,6-diethylaniline) and 10 to 20 parts byweight diethyl 2,4-toluenediamine, and most preferably 85 parts byweight 4,4′ methylene-bis-(3-chloro-2,6-diethylaniline) and 15 parts byweight diethyl 2,4-toluenediamine.

The second mixture is preferably utilized to prevent the diisocynatefrom “flashing off” during the processing. The second mixture providesheat stability to the diisocynate during the processing. The secondmixture also allows the temperature of the reaction to be reducedsubstantially which provides for a more favorable viscosity. Further,the use of 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) allows forthe diisocynate to be utilized at a higher temperature since the 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) essentially increasing theboiling temperature of the diisocynate.

Preferably, the diamines comprises between 1% to 10% of the total weightof the mixture forming the cross-linked thermoplastic polyurea. Evenmore preferably, diamine comprises between 1% to 2% of the total weightof the mixture forming the cross-linked thermoplastic polyurea. Diaminesother than those specifically identified above may also be used inaccordance with the invention, provided they exist as a solid at atemperature within the range of 50° F. to 150° F.

In an alternative embodiment, hydroquinone (HQEE) replaces the diamineconstituent and is added to the mixture of MDI and thermoplasticurethane. As with the prior embodiment, HQEE is added to the mixture insolid form and dry blended with the MDI and thermoplastic urethane basematerial. In yet another alternative embodiment, HQEE is added inconjunction with a diamine.

The mixture of thermoplastic urethane base material, MDI, and diamine(and/or HQEE) is then mixed and heated to a temperature within the rangeof 250° F. to 550° F. The solid thermoplastic urethane base material,MDI, and diamine (and/or HDEE) melt and partially cross-link.Preferably, the partially cross-linked thermoplasticpolyurethane/polyurea is post-cured by heating the same to a temperaturewithin the range of 150° F. to 250° F. for a period of time rangingbetween 2 and 36 hours.

FIG. 1 illustrates an injection molding device 10 capable of producingcross-linked thermoplastic polymers in accordance with the presentinvention. The injection molding device 10 includes a hopper 12 forloading the various components (e.g., a first mixture of thermoplasticurethane resins and MONDUR flakes). The hopper 12 preferably includes arotating mixer therein for dry mixing the first mixture materials.

The hopper 12 is in flow communication with a mixing barrel 16 having ascrew (not shown). The screw is disposed inside the mixing barrel 16,and both rotates and reciprocates within the mixing barrel 16. Thedistal end of the mixing barrel 16 terminates into an injection chamberand injection nozzle. The injection nozzle is preferably disposed insidea stationary platen and is in flow communication with a mold 18. Themold 18 preferably includes one or more cavities (not shown) having apre-formed shape. The injection molding device 10 may be used to formany number of products including, for example, skateboard wheels,in-line skate wheels, roller coaster wheels, caster wheels, golf balllayers, and golf club components, and the like. Products in theautomotive industry such as seals, O-rings, gaskets, bushings, CV-jointcover, and tires may also be made using the methods described herein.For agricultural applications, the methods can be used in silo liners,plow parts, pipe, and pipe liners. The invention also has utility inmining applications, where the methods and processes described hereincan be used to produce mining screens, material moving buckets, pumpparts and liners, pulleys, and bumpers. The materials and methods canalso be used in footwear applications such as, for example, shoe solesand the like. The invention can also be used in general purposeapplications such as press pads, abrasion-resistant silo or hopper linersheets, gears, hammers, metal forming parts, etc. The injection moldingdevice also includes a secondary mixing chamber 20 for mixing andheating a second mixture for introduction into the barrel 16. Thesecondary mixing chamber 20 is in flow communication with the barrel 16through a flow pipe 22.

FIG. 2 is a flow chart of a preferred method 200 of the presentinvention. At block 202, the thermoplastic polyurethane (“TPU”) resinand a diisocynate are mixed to create a first mixture. The monomericdiisocynate comprises between 1% to 10% of the total mass of the firstmixture, and most preferably 6% by weight of the first mixture.Preferably the diisocynate is MONDUR flakes. At block 204, 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) and diethyl2,4-toluenediamine are mixed to create a second mixture. The secondmixture is preferably mixed in the secondary mixing chamber 20 asdescribed in reference to FIG. 1. The 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) is preferably 75% to 95% ofthe total mass of the second mixture and diethyl 2,4-toluenediamine is25% to 5% of the total mass of the second mixture. At block 206, thefirst mixture is heated to create a first heated mixture. The firstmixture is heated to a temperature preferably within the range of 250°F. to 550° F. to create a heated first mixture. At block 208, the secondmixture is heated to create a liquid second mixture. The liquid secondmixture is preferably created in the secondary mixing chamber 20. Thesecond mixture is preferably heated to a temperature greater than themelting point of the second mixture and less than 225° F. to create aliquid second mixture having a predetermined volume. At block 210, theheated first mixture is injected into a barrel through an opening at oneend of the barrel, preferably the barrel 16 as described in reference toFIG. 1. At block 212, the liquid second mixture is injected into thebarrel at predetermined intervals and in predetermined amounts. In apreferred embodiment, the liquid second mixture is injected into thebarrel four times in four equal amounts of the volume of the liquidsecond mixture in order to create a homogeneous reaction product. Eachof the four injections of the liquid second mixture is preferably 1 to20 grams of the liquid second mixture. At block 214, the reactionproduct is injected into a mold cavity, preferably a cavity of a mold 18as described in reference to FIG. 1. At block 216, an article is formedfrom the reaction product within the mold 18. The article is preferablyan article such as discussed above.

The following are experimental test results of various cross-linkedthermoplastic urethanes/ureas in accordance with the present invention.Example 1 is a control of TEXIN DP7-1197 thermoplastic polyurethane.Example 2 is TEXIN DP7-1197 thermoplastic polyurethane crosslinked at2/2. Example 3 is TEXIN DP7-1197 thermoplastic polyurethane crosslinkedat 2/3. Example 4 is TEXIN DP7-1197 thermoplastic polyurethanecrosslinked at 2.5/3. Example 5 is a control of DESMOPAN 445thermoplastic polyurethane. Example 6 is DESMOPAN 445 thermoplasticpolyurethane crosslinked at 2/2. Example 7 is DESMOPAN 445 thermoplasticpolyurethane crosslinked at 2/3. Example 8 is DESMOPAN 445 thermoplasticpolyurethane crosslinked at 2.5/3. Example 9 is DESMOPAN 445thermoplastic polyurethane crosslinked at 2.5/5. Example 8 is DESMOPAN445 thermoplastic polyurethane crosslinked at 2.5/7. The thermoplasticpolyurethanes crosslinked according to the present invention (Examples2-4 and 6-10) demonstrate much better properties than the controlsamples (Examples 1 and 5).

TABLE ONE TEST 1 2 3 4 5 6 7 8 9 10 Tensile Test- 885 psi 1007 1042 10741499 1566 1715 1714 1849 2090 ASTM D 412- Die C-strength at 100%elongation Tensile Test- 2004 psi 2239 2360 2447 2360 2514 3046 30153232 3736 ASTM D 412- Die C-strength at 300% elongation Tensile Test-675% 598 621 619 641 547 510 499 422 364 ASTM D 412- Die C-ultimateelongation Tensile Test- 6040 psi 6212 6963 6493 4109 3799 4714 46844325 4396 ASTM D 412- Die C-ultimate tensile strength Die “C” Tear 686pli 676 641 615 706 710 707 693 702 715 ASTM D 624- D 3489-tearresistance Durometer 89 90 90 91 94 94 94 94 96 97 Hardness, ShoreA-ASTM D 2240- hardness at 5 secs. Durometer 31 33 34 34 37 39 39 39 4244 Hardness, Shore D- ASTM D 2240- hardness at 5 secs. Vicat Softening129° C. 145 152 152 141 147 158 159 162 166 (10 N load, 50 C. rate ofrise) ASTM D 1525- softening temperature Compression  34% 28 23 18 28 2220 17 15 15 Set, Test Meth B, 25% Defl., 70 C., 22 hrs, ASTM D 395-percent set Compression  13% 17 9 9 13 14 9 11 12 12 Set, Test Meth B,25% Defl., RT, 22 hrs, ASTM D 395- percent set

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this invention andwill readily understand that while the present invention has beendescribed in association with a preferred embodiment thereof, and otherembodiments illustrated in the accompanying drawings, numerous changes,modifications and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this invention which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claims. Therefore, the embodiments of the inventionin which an exclusive property or privilege is claimed are defined inthe following appended claims.

1. A method for forming a golf ball layer composed of a cross-linkedthermoplastic polymer, the method comprising: mixing a thermoplasticurethane based material and a monomeric diisocyanate to create a firstmixture, the monomeric diisocynate comprising between 1% to 10% of thetotal mass of the first mixture; mixing 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) and diethyl2,4-toluenediamine to create a second mixture, wherein the 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) is 75% to 95% of the totalmass of the second mixture and diethyl 2,4-toluenediamine is 25% to 5%of the total mass of the second mixture; heating the first mixture to atemperature within the range of 250° F. to 550° F. to create a heatedfirst mixture; heating the second mixture to a temperature greater thanthe melting point of the second mixture and less than 225° F. to createa liquid second mixture having a volume; injecting the heated firstmixture into a barrel of an injection molding machine through a firstopening; injecting the liquid second mixture into the barrel of theinjection molding machine in a plurality of dispensing shots ofapproximately equal amounts of the volume of the liquid second mixtureduring a predetermined time period; injecting a reaction product into atleast one injection mold cavity, the reaction product formed by thereaction of the heated first mixture and the liquid second mixture; andforming a golf ball layer composed of the reaction product.
 2. Anapparatus for forming a golf ball layer composed of a cross-linkedthermoplastic polymer, the apparatus comprising: a hopper for mixing athermoplastic urethane based material and a monomeric diisocyanate tocreate a first mixture, the monomeric diisocynate comprising between 1%to 10% of the total mass of the first mixture, wherein the first mixtureis heated within the hopper to a temperature within the range of 250° F.to 550° F. to create a heated first mixture; a mixing chamber for mixing4,4′ methylene-bis-(3-chloro-2,6-diethylaniline) and diethyl2,4-toluenediamine to create a second mixture, wherein the 4,4′methylene-bis-(3-chloro-2,6-diethylaniline) is 75% to 95% of the totalmass of the second mixture and diethyl 2,4-toluenediamine is 25% to 5%of the total mass of the second mixture, wherein the second mixture isheated to a temperature greater than the melting point of the secondmixture and less than 225° F. to create a liquid second mixture having avolume; a barrel having a first opening in flow communication with thehopper for receiving the heated first mixture, the barrel in flowcommunication with the mixing chamber for receiving injections of theliquid second mixture into the barrel in a plurality of dispensing shotsof approximately equal amounts of the volume of the liquid secondmixture during a predetermined time period; at least one injection moldcavity in flow communication with the barrel to receive the reactionproduct formed by the reaction of the heated first mixture and theliquid second mixture and to form a golf ball layer composed of thereaction product.